SRC/slaed0.f(3)

NAME
SRC/slaed0.f

SYNOPSIS

  Functions/Subroutines
subroutine slaed0 (icompq, qsiz, n, d, e, q, ldq, qstore, ldqs, work, iwork, info)
SLAED0 used by SSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Function/Subroutine Documentation

  subroutine slaed0 (integer icompq, integer qsiz, integer n, real, dimension( * ) d, real, dimension( * ) e, real, dimension( ldq, * ) q, integer ldq, real, dimension( ldqs, * ) qstore, integer ldqs, real, dimension( * ) work, integer, dimension( * ) iwork, integer info)

SLAED0 used by SSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Purpose:

    !>
    !> SLAED0 computes all eigenvalues and corresponding eigenvectors of a
    !> symmetric tridiagonal matrix using the divide and conquer method.
    !>

Parameters
    ICOMPQ

    !>          ICOMPQ is INTEGER
    !>          = 0:  Compute eigenvalues only.
    !>          = 1:  Compute eigenvectors of original dense symmetric matrix
    !>                also.  On entry, Q contains the orthogonal matrix used
    !>                to reduce the original matrix to tridiagonal form.
    !>          = 2:  Compute eigenvalues and eigenvectors of tridiagonal
    !>                matrix.
    !>

    QSIZ

    !>          QSIZ is INTEGER
    !>         The dimension of the orthogonal matrix used to reduce
    !>         the full matrix to tridiagonal form.  QSIZ >= N if ICOMPQ = 1.
    !>

    N

    !>          N is INTEGER
    !>         The dimension of the symmetric tridiagonal matrix.  N >= 0.
    !>

    D

    !>          D is REAL array, dimension (N)
    !>         On entry, the main diagonal of the tridiagonal matrix.
    !>         On exit, its eigenvalues.
    !>

    E

    !>          E is REAL array, dimension (N-1)
    !>         The off-diagonal elements of the tridiagonal matrix.
    !>         On exit, E has been destroyed.
    !>

    Q

    !>          Q is REAL array, dimension (LDQ, N)
    !>         On entry, Q must contain an N-by-N orthogonal matrix.
    !>         If ICOMPQ = 0    Q is not referenced.
    !>         If ICOMPQ = 1    On entry, Q is a subset of the columns of the
    !>                          orthogonal matrix used to reduce the full
    !>                          matrix to tridiagonal form corresponding to
    !>                          the subset of the full matrix which is being
    !>                          decomposed at this time.
    !>         If ICOMPQ = 2    On entry, Q will be the identity matrix.
    !>                          On exit, Q contains the eigenvectors of the
    !>                          tridiagonal matrix.
    !>

    LDQ

    !>          LDQ is INTEGER
    !>         The leading dimension of the array Q.  If eigenvectors are
    !>         desired, then  LDQ >= max(1,N).  In any case,  LDQ >= 1.
    !>

    QSTORE

    !>          QSTORE is REAL array, dimension (LDQS, N)
    !>         Referenced only when ICOMPQ = 1.  Used to store parts of
    !>         the eigenvector matrix when the updating matrix multiplies
    !>         take place.
    !>

    LDQS

    !>          LDQS is INTEGER
    !>         The leading dimension of the array QSTORE.  If ICOMPQ = 1,
    !>         then  LDQS >= max(1,N).  In any case,  LDQS >= 1.
    !>

    WORK

    !>          WORK is REAL array,
    !>         If ICOMPQ = 0 or 1, the dimension of WORK must be at least
    !>                     1 + 3*N + 2*N*lg N + 3*N**2
    !>                     ( lg( N ) = smallest integer k
    !>                                 such that 2^k >= N )
    !>         If ICOMPQ = 2, the dimension of WORK must be at least
    !>                     4*N + N**2.
    !>

    IWORK

    !>          IWORK is INTEGER array,
    !>         If ICOMPQ = 0 or 1, the dimension of IWORK must be at least
    !>                        6 + 6*N + 5*N*lg N.
    !>                        ( lg( N ) = smallest integer k
    !>                                    such that 2^k >= N )
    !>         If ICOMPQ = 2, the dimension of IWORK must be at least
    !>                        3 + 5*N.
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit.
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value.
    !>          > 0:  The algorithm failed to compute an eigenvalue while
    !>                working on the submatrix lying in rows and columns
    !>                INFO/(N+1) through mod(INFO,N+1).
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Contributors:
    Jeff Rutter, Computer Science Division, University of California at Berkeley, USA

Definition at line 170 of file slaed0.f.

Author

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